Turning lathe motor from forward to reverse

[Jim Ferrous]

My switch can turn my lathe motor instantly from forward to reverse.

How bad is this for an electric motor? I'm guessing bad????

[Stustoys]

Is it a single phase lathe?

With 3 phase motors(depending on the motor of course) there is a limit to the number of times you can do this an hour. The current must be pretty impressive.

Stuart

[Big Shed]

The Sieg C6/H&F AL60 uses a 550w AC motor. It has a Fwd/Rev switch similar to the one on my SM920V, these switches have an Off position in between the Fwd/Rev position.

So electrically the motor is switched off before changing direction, but that doesn't mean that the chuck has physically stopped before the motor changes direction.

When I need to use the Rev function, usually when cutting a thread, I always ensure the work has stopped before changing direction.

I can't foresee a situation where you would change direction without ensuring the work has stopped, it wouldn't be that good for the motor, nor would it be that good for the gears etc.

I wouldn't do that in my car, so why on the lathe?

[Stustoys]

Oh in that case. Are you sure its reversing?
I discovered(or rediscovered?) just lately that "throwing the lathe into reverse" with a single phase cap start motor does nothing unless it slowed enough between Fwd and Rev for the centrifugal switch to close. If it doesn't close the motor just keeps running in the same direction(with the switch in Rev).

Stuart

[.RC.]

If the motor is well made probably not a lot of damage if done intermittently...

Of course if it is an aggressive change of direction and the spindle is a screwed nose, you could reverse the chuck off...

This is where foot brakes come in handy, to stop the motor quickly, then reverse....

[th62]

I think Stustoys is right: from my experience, turning the switch from forward to reverse, or vice versa, does nothing other than make a very loud clunking noise, the motor will continue in the same direction. The motor must be stopped and then re-started to get the motor to start in the opposite direction.

[Jim Ferrous]

No it doesn't keep going in the same direction. It's instantaneously turns, that's why was thinking it can't be good for an electrical motor.

[BobL]

Is it a 3 phase motor?

When I did it accidentally on my lathe with a SAJ VFD I noticed that the lathe took the same time as usual to slow down and stop and only then did it turn the other way.
It's like the VFD has control over the process.

[simonl]

It's probably not good on a number of levels. Just don't do it! :doh:

Simon

[mahgnia]

The motor on my C6 is a single phase capacitor start motor, and quick operation of the reverse switch will give a slight pause but the motor continues in the same direction if it hasn't slowed down.
This would be the expected behaviour for this type of motor as the capacitor has not been switched into the circuit until the motor slows down.
I wouldn't be switching from forward to reverse without allowing the motor to stop in between due to the high extra load on the motor and the electrical supply circuit/fuse:no:.

Andrew

[Ueee]

Is it a brushed motor? That might be the only way it could happen unless of course its 3 phase.....

Ew

[andrew_mx83]

It's like the VFD has control over the process.

Correct. The VFD slows and stops the motor, then starts it up again in reverse instantly. I still prefer to wait a second in between as you can hear it pick up the lash in the geartrain as it restarts otherwise.

[Stustoys]

Correct.
As long as the VSD is set to controlled stop with dc braking.

Playing with settings would likely stop the noise if you really wanted(dc braking at start springs to mind)

Stuart

[jackaroo]

If its 3 phase then you can do it.
if single phase (and reversible) I think it will keep going on the same direction unless the motor is fully stopped then turn on reverse.